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Soil tillage effects on the efficacy of cultivars and their mixtures in winter barley
Field Crops Research 128 (2012) 91–100
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Soil tillage effects on the efficacy of cultivars and their mixtures in winter barley A.C. Newton a,∗ , D.C. Guy a , A.G. Bengough a,b , D.C. Gordon a , B.M. McKenzie a , B. Sun a , T.A. Valentine a , P.D. Hallett a a b
The James Hutton Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK Division of Civil Engineering, University of Dundee, Dundee DD1 4HN, UK
a r t i c l e
i n f o
Article history: Received 5 August 2011 Received in revised form 9 December 2011 Accepted 13 December 2011 Keywords: Blends Cultivation Mildew Rhynchosporium Disease Yield
a b s t r a c t Cereal farming is moving rapidly towards reduced tillage, with over 100 million ha of land currently tilled using minimum tillage implements. This study reports five years of data from a field experiment investigating the response of different barley cultivars and mixtures to soil tillage practice and nitrogen fertiliser levels. Five tillage treatments were established that imposed different amounts of soil disturbance: (T1) zero tillage, (T2) minimum tillage to 7 cm depth and ploughed treatments followed by power harrowing consisting of (T3) conventional plough to 20 cm depth, (T4) plough to 20 cm followed by compaction by wheeling the entire plot with a tractor fitted with 8.8 Mg total load and (T5) deep plough to 40 cm depth, all on the same site each year. Four winter barley cultivars (Sumo, Fanfare, Pastoral and Pipkin) were selected based on contrasting rooting characteristics, disease resistance and yield sensitivity. They were planted in plots as monocultures and as all 2-, 3- and 4-component mixtures thereof. Significant differences in soil physical properties and carbon content were observed over the five years of the study. Grain yield varied by 13% between tillage treatments, with conventional and deep plough conditions generally the highest yielding and zero tillage the lowest. Sumo gave the highest yield overall under deep plough conditions, whereas Pipkin was the best cultivar under conventional and zero tillage conditions. Rhynchosporium was the most common disease and the mixture gave decreased infection in all years and tillage conditions. Complex mixtures gave around 32% less disease than the simple mixtures. There was an overall differential cultivar response to soil tillage conditions that was buffered by cultivar mixtures. Mixtures offered benefits in both yield response and disease control under all soil tillage conditions. © 2011 Elsevier B.V. All rights reserved.
1. Introduction There have been several comparisons of yield performance of cereals under different tillage regimes and disease incidence has been monitored for some of these (e.g. Riley et al., 2005; Melero et al., 2009). Such research is vital to understanding crop responses to evolving farming practices, as the large shift towards conservation tillage in semi-arid climates has not occurred to the same extent in the cool and humid areas of Europe. Rieger et al. (2008) attributed this slower adoption to a lack of knowledge about agronomic and ecological impacts. Most European breeding trials are based on soils cultivated to at least 20 cm depth with a pass from both plough and harrow, whereas over 100 million ha of farmland is tilled using single pass minimum tillage implements to <10 cm or direct-drilling (Verch et al., 2009). Less intense tillage can have a large impact on the root environment, particularly mechanical impedance, aeration and plant available water in soil (Betz et al.,
∗ Corresponding author. Tel.: +44 1382 568824. E-mail address: [email protected] (A.C. Newton). 0378-4290/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2011.12.004
1998). Plant traits that respond well to these conditions may be different from those selected in breeding trials using intensive tillage. For instance, reduced tillage preserves continuous macro- and biopores in soil, which some cereal cultivars may exploit better than others (McKenzie et al., 2009). Another major difference between ploughing and reduced tillage is the distribution of plant debris on the soil surface and in the topsoil (Wang and Dalal, 2006). Plant root growth is likely to be affected greatly by differences in soil physical conditions such as compaction, plough pans and continuity of macro- and micro-pores. High soil disturbance will enable roots to access water at greater depth for example (McKenzie et al., 2009). Compaction will increase mechanical impedance to rooting (Bengough, 1997; Atkinson et al., 2007). Therefore differences between cultivars in their root morphological traits such as their length, depth and angle might result in differential performance under different tillage treatments. The advantages of cultivar mixtures in minimising disease and increasing yield compared with the mean of their monocultures, and providing yield stability, are well established (Finckh et al., 2000; Wolfe, 1985; Mundt, 2002; Newton et al., 2009). The disease control trait is particularly advantageous where zero or low
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use of synthetic pesticides is permitted such as in organic or low input systems respectively. Much of the published data on mixtures of cereals is from various conventional farming systems characterised by intensive soil tillage by ploughing and high levels of synthetic inputs. Given shifts towards reduced tillage and fertiliser use, enhanced crop function may be required and may be achieved through deployment of diversity, and specifically through the use of cultivar mixtures (Newton et al., 2009). In general, where plant debris is the source of inoculum, burying it by ploughing reduces foliar diseases (Montanari et al., 2006; Yarham, 1975). However, in other reports disease incidence was independent of tillage methods (Rasmussen, 1988), probably because the effects of previous crops and their disease incidence and severity was greater (Turkington et al., 2006). This demonstrated the increased importance of crop rotation, particularly in reduced tillage situations (Arvidsson, 1998). The severity of eyespot (Oculimacula yallundae) under minimum versus conventional tillage conditions has been observed to decrease over successive minimum tillage seasons (Brooks and Dawson, 1968) and whilst this is partly explained by differences in plant habit under the different cultivation conditions (Yarham and Norton, 1981) it may also be due to establishment of an equilibrium between pathogens and their antagonists (Kuntzsch, 1990; Jamaluddin and Jenkyn, 1996; Burnett and Hughes, 2004). The incidence of rhynchosporium caused by Rhynchosporium secalis infection on barley is clearly increased by reduced cultivation as crop debris from previous crops is not buried (Turkington et al., 2006; Arvidsson, 1998; Yarham, 1975). Growing barley in mixtures has been shown to decrease rhynchosporium severity (Jaeger et al., 1981; Horoszkiewicz-Janka and Michalski, 2003; Olsen et al., 1986; Newton et al., 1997, 2008a, 2008b; Newton and Guy, 2008). However, the relative performance of cultivar mixtures under different tillage regimes has been determined for neither yield nor disease control traits. Nor is it known whether the severity of R. secalis infection changes as inoculum and any antagonists establish in reduced tillage systems across successive years. Most mechanistic studies of cultivar mixtures have concerned the aerial environment and foliar pathogens. Whilst this is appropriate for epidemiological studies of leaf pathogens, particularly if the soil surface debris and its environment are taken into consideration, for yield studies resource capture above ground is clearly only a part of the crop production system. Efficiency of water and nutrient capture from the soil may be a critical component of differences between cultivars, and interactions between different rooting strategies a key to understanding overall mixtures performance. Therefore cultivars with different rooting characteristics need to be assessed individually and in interactions, and contrasting root environments such as those created by different cultivation regimes should be used to vary the potential for expressing the benefits of these different characteristics. This paper reports five years of data from a field investigation of the response of barley cultivars with contrasting root, disease resistance and other agronomic traits, grown singly and in mixtures, to soil tillage practice and nitrogen fertiliser levels. There were five soil tillage practices used, which cultivated soil to a range of depths from 0 cm (no-till) to 40 cm (deep plough). One ploughed treatment was also compacted by wheeling. This produced differences in the soil environment experienced by crop roots, thereby enabling study of the genotype × environment interactions of a range of barley lines and mixtures thereof. We hypothesised that cultivars would differ in their response to tillage treatments and that the mixtures would confer greater resilience to changes in tillage practice, resulting in greater and more stable yield under shallow cultivation. The cultivar response differences might be correlated with root trait differences and the mixtures advantage might be attributable to a combination of enhanced resistance to disease spread and
increased tolerance of soil conditions from complementarity of contrasting root traits. 2. Materials and methods 2.1. Root and shoot characteristics Based on the UK Recommended List of Cereals (hgca.com) published variety characteristics of height, standing power, earliness, yield sensitivity, powdery mildew resistance and rhynchosporium resistance, cultivars were selected with contrasting traits. These were characterised for total seedling root length, average longest root, average shoot length, and average root angular spread using a gel observation chamber described by Bengough et al. (2004). It consisted of 2 mm thick layers of water agar on flat sheets, 300 mm height by 215 mm width that were separated by a 2 mm thick airgap when placed together. Roots were grown in the gap and a Perspex front face allowed observation of the roots. After 10 days the chambers were scanned at a resolution 800 dpi and the root characteristics were analysed with Scion image software. Using all these traits, but with an emphasis on root traits, four cultivars were selected for contrasting traits (Fig. 3 and Table 1), namely Fanfare, Pastoral, Pipkin and Sumo. 2.2. Soil characteristics Soil conditions were manipulated in a field experiment by using different forms of tillage. The soil was a Dystric-Fluvic Cambisol with a sandy-loam surface texture (Bell and Hipkin, 1988). It had a pH of 5.7, was freely drained and underlain by colluvial sand at 60 cm depth. To minimise in-field variability the entire site was first uniformly ploughed to 20 cm, power harrowed and sown with the spring barley variety (var. Optic) in spring 2003 (year 0). Auger holes were dug to 50 cm at 20 random locations across the experiment site to observe depth of the plough layer (Ap), plough pans and the nature of the subsoil sediment. In July, baseline measurements of soil carbon and nitrogen were determined on samples taken at 0–10 cm depth on a 4 × 4 evenly spaced grid that covered the entire experimental field. At each point on the grid, sampling was done at five nearby locations and then mixed. Soils were dried at 105 ◦ C, ball-milled and then measured using a continuous flow mass spectrophotometer consisting of an ANCA SL sample converter attached to a 20-20 IRMS (Europa Scientific, Crewe, UK) in 2003 and 2004, and with an Exeter Analytical CE440 Elemental Analyzer (EAI, Coventry, UK) in 2008. Prior to harvest, blocks corresponding to the subsequent experiment layout shown in Fig. 1 were marked out and the barley was harvested from each block to approximate yield and the evenness of the site. 2.3. Treatments and trial design Five tillage treatments were established in autumn 2003 that imposed different levels of soil disturbance: (T1) zero tillage, (T2) minimum tillage to 7 cm depth and ploughed treatments followed by power harrowing consisting of (T3) conventional plough to 20 cm depth, (T4) plough to 20 cm followed by compaction by wheeling the entire plot with a Massey Ferguson 6270 tractor fitted with 16.9R-38 rear tyres (8.8 Mg total load, 2.9 Mg wheel load and 110 kPa contact pressure) and (T5) deep plough to 40 cm depth. These treatments were selected to provide different physical constraints to root growth and water availability. Fifteen blocks each 33 × 33 m were marked out in an even grid with five blocks in each of three north-south columns representing the three treatment replicates. Blocks were separated from each other by strips at least 3 m wide that were sown with grass seed after the first trial year was sown (Fig. 1).
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Fig. 1. Layout of soil tillage treatments 2003–2008 and the yield (kg) of spring barley in year 0 prior to treatments being applied.
Within each of the 15 blocks, a split block trial was sown. There were 15 trial entries comprising the four monocultures, all six 2component, all four 3-component and the 4-component mixture in equal proportions adjusted by thousand grain weights (Table 1). Plots measured 1.55 m wide × 6.0 m long, reduced to 4.8 m harvested length by plot definition, and were sown at 360 seed/m2 with an eight-row Hege plot drill with five plots per bed. Three replicates and two fertiliser levels were used, N1 = half rate and N2 full rate 180 kgN/ha, P, K) applied as top dressings in April and again in May (Fig. 2). In 2008 the N1 treatment was discontinued
but the N2 (full rate) was sown as before. The trial was sown in five successive years and whilst the randomisations were different for every block, identical randomisations were used each year so that the same monoculture or mixture was sown in the same place every year. No fungicide treatments were applied to the plots. Each year all plots were harvested when ripe using a Wintersteiger plot combine, and the grain was dried to constant moisture and weighed. In 2004, 2005, 2006 and 2008 the thousand grain weights were assessed. Straw was removed from all of the plots following harvest.
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Table 1 Characteristics of winter barley varieties selected for mixtures trialling. Cultivars/mixtures
Agronomy
Disease resistance
Yield
Shortness
Standing
Earliness
Rhynchosporium
Mildew
Sensitivity
Sumo Fanfare Pastoral Pipkin
7a 7 7 7
7a 5 7 4
5a 5 6 5
5a 8 8 3
6a 5 5 2
1.06b 0.84 0.97 0.80
2 component mixtures (6): 3-component mixtures (4): 4-component mixture (1):
Sumo-Fanfare, Sumo-Pastoral, Sumo-Pipkin, Fanfare-Pastoral, Fanfare-Pipkin, Pastoral-Pipkin Sumo-Fanfare-Pastoral, Sumo-Fanfare-Pipkin, Sumo-Pastoral-Pipkin, Fanfare-Pastoral-Pipkin Sumo-Fanfare-Pastoral-Pipkin
a b
Strength of trait expression on a 1 (low) to 9 (high) scale. HGCA UK Recommended Lists for cereals: Cereal variety handbook (HGCA, 1999, 2001). Above 1 = cultivar more sensitive than average to changes in site yield; below 1 = cultivar has below average response to changes in site yield (HGCA, 1999, 2001).
2.4. Assessments and analysis Diseases were scored on a 1-9 whole plant severity scale (Newton and Hackett, 1994) when above trace levels, and scored again at approximately two-weekly intervals. Scores were converted to percentage infection and the Area Under the Disease Progress Curve (AUDPC) calculated. At the beginning of the first growing season in April 2004 and the end of the final growing season in October 2008, 56 mm diameter × 40 mm height soil cores were sampled from 2 to 7 cm depth at 3 random locations in each experimental block to determine soil dry bulk density. Soil water release was measured as a function of soil matric potential for these soil samples using a tension table and pressure plate apparatus (Townwend et al., 2001). Plant available water content was determined as the difference between volumetric water content at a matric potential of −1.5 MPa (wilting point) and at −0.5 kPa (field capacity). Disturbed soil samples were collected from the same locations from 0 to 10 cm for carbon measurements. pH was measured on a 1:5 soil:water mix. Penetration resistance was measured at three random locations in each block at the start of the first growing season. Measurements were done to a depth of 40 cm at 2 cm
N1
N2
N1
N2
Guard T-rep 1
T-rep 2
Guard 2
N2
Guard
N1
T-rep 3
Fig. 2. Treatment design within a replicate block. T-rep = replicate within a treatment and block. Guard = Sumo. Guard 2 = Pastoral. Trial entry plots: 1350 in total, 450 within a replicate block.
increments using a Rimik Cone Penetrometer (Rimik, Toowoomba, Australia). Analysis of variance was carried out using Genstat eleventh edition for Windows (VSN International Ltd, Hemel Hemstead, UK) using a split-split plot model with tillage treatment as the main plot, nitrogen as the sub-plot, and cultivar as the sub-sub-plot. A set of contrasts were set up to test monoculture compared with mixtures effects where required (Newton et al., 2008a). For comparing mixtures, the cultivars were grouped into monocultures, 2-component (simple) mixtures, and the 3-component and the 4component (complex) mixtures together for further analysis. These were analysed using analysis of variance and series of contrasts were calculated from the variety means to test the significance of particular comparisons, such as monocultures versus 2-component mixtures, balanced so that each variety had equal weight in all comparisons. 3. Results 3.1. Experimental site and seasons The area of land chosen for this experiment shown in Fig. 1 illustrates unevenness in crop yield from west to east, highlighted by how different replicate 3 was from replicates 1 and 2 in yield of the year 0 spring barley crop, a difference of around 10% that was significant when treated as a factor (p = 0.003). However, there were no significant differences (p = 0.646) between the areas chosen for the five treatments overall, the mean yields differing by only 36 kg (LSD = 55 kg), illustrating the utility of the randomisation in the treatment design. The baseline soil data for water content (14.3 ± 1.4 g 100 g−1 s.e.), carbon (2.5 ± 0.03 g 100 g−1 s.e.) and nitrogen (0.2 ± 0.01 g 100 g−1 s.e.) were similar across the experimental site (p > 0.10). Auger holes to 50 cm depth showed similar thicknesses of the top soil horizon (Ap). However, data from the soil survey (Bell and Hipkin, 1988) and our auger samples to 50 cm depth identified ingress of colluvial sediment in the subsoil that is more pronounced moving from east to west. A plough pan at 20–25 cm depth was observed across the entire experimental site. In 2004, 2005, 2007 and 2008 harvest years all field operations were carried out successfully. For the 2006 season it was exceptionally wet at time of sowing (data not shown) and the minimum and zero tillage treatments were the first to be accessible and were sown in early November. It was not until early December that the ground became accessible for ploughing and the other three treatments were sown. Poor establishment and subsequent winter conditions lead to severe seedling mortality, so although disease assessments and yield measurements were made and there was continuity of cropping, these data are treated differently or excluded from many analyses.
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95
(a)
50
10
40
8 30
6 4
20
2
10
0
0
0.16 0.14
Root:Shoot Ratio
60
0.12
140 Root:Shoot
(b)
Angle
120 100
0.10
80
0.08 60
0.06 0.04
40
0.02
20
0.00
o
Length (cm)
12
Depth Length
Angle ( )
14
Total Length (cm)
70
16
0 Fanfare
Pastoral
Pipkin
Sumo
Fig. 3. Root characteristics of seedlings of the different barley cultivars after 10 days growth in a gel observation chambers. The root lengths and anglular spread were measured and the longest root length:shoot length ratio was calculated.
The root characteristics of the seedlings of the selected barley cultivars are shown in Fig. 3. Root angle and the total length of all roots were different between the cultivars (p < 0.01), but depth was similar. Stem height and hence longest root length:shoot length ratio also varied (p < 0.01), with both traits 40% greater in Sumo than Fanfare (Fig. 3). From these tests of seedlings in laboratory conditions, variable root and shoot characteristics between cultivars were identified and, together with above-ground characteristics from Recommended List data shown in Table 1 (HGCA, 1999, 2001), the four cultivars shown were selected for contrasting combinations. 3.3. Soil properties The different forms of tillage applied influenced soil physical conditions in the first year of the experiment. Penetration resistance measured in April was markedly different between plots, with deep plough having the least impedance to root growth, whereas zero and minimum tillage had greatest impedance in the topsoil and would impede root growth (resistance >2 MPa) below 180 mm (Fig. 4). By contrast the depth or impeded growth under deep plough treatment was 280 mm. On soil cores sampled from 2 to 7 cm depth at the start of the first growing season there was no difference in field capacity (25.5 ± 0.82 g 100 g−1 ) or bulk density (Table 2) between treatments (p > 0.05). Plant available water in both deep plough (13.2 ± 0.39 g 100 g−1 ) and compaction (13.4 ± 0.32 g 100 g−1 ) was about 2 g 100 g−1 less (p < 0.001) than in plough (15.2 ± 0.48 g 100 g−1 ), minimum tillage (15.2 ± 0.30 g 100 g−1 ) and zero tillage (15.9 ± 0.29 g 100 g−1 ). At the start of the experiment, soil carbon concentration was decreased under deep plough, with the effect exacerbated by the end of the experiment (Table 2).
Cultivar also showed highly significant interaction with both tillage and year (p < 0.001), and the cultivar × year × nitrogen interaction was also significant (p = 0.003). This reflected the changed behaviour between the first two establishing years and the later years of the experiment. Overall the standard nitrogen treatment increased yield by 25% over the half rate treatment, and yield varied by 13% between tillage treatments. Conventional and deep plough conditions were generally the highest yielding and zero tillage the lowest under either nitrogen treatment (Fig. 5, Table 5). However, the trend across the years was for the three high disturbance conditions to behave similarly whilst the yield from the minimum tillage decreased progressively and the yield from zero tillage decreased faster still (Fig. 5). The exception was 2006 when both low disturbance treatments yielded less than previous years but better than the high disturbance for the reasons given above. Overall, the mean yield across the years varied by only 9% excluding 2006. The four monocultures had relatively consistent yield across the different tillage treatments overall, though Pastoral appeared to yield relatively better under reduced tillage with minimum tillage ranking higher and deep plough ranking lower than with the other
0 Compacted Deep Plough Minimum Tillage Zero Tillage Plough
100
Depth (mm)
3.2. Root and shoot characteristics
200
300
400
3.4. Yield and thousand grain weight Tillage, year, nitrogen and cultivar effects on yield were highly significant overall (p < 0.001) but there were highly significant interactions between year and tillage, and year and nitrogen.
0
1
2
3
4
Penetration Resistance (MPa) Fig. 4. Penetration resistance measured in April 2004 after the first year of establishing the experiment. Error bars show +/− standard error of the means.
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Table 2 Soil characteristics at the start of the first and end of the final growing season. Tillage treatment
Year 1 (2004) Carbon, g 100 g−1
Zero tillage Min. tillage Plough Compaction Deep plough
2.79 2.84 2.72 2.88 2.56
p
0.04
± ± ± ± ±
0.08 0.10 0.04 0.08 0.06
Year 5 (2008) Bulk density, g cm−3
Carbon, g 100 g−1
1.32 ± 0.03 1.30 ± 0.02 1.32 ± 0.01 1.33 ± 0.02 1.33 ± 0.02
2.65 2.82 2.56 2.58 2.25
n.s.
<0.01
± ± ± ± ±
0.02 0.05 0.02 0.04 0.03
Percentage change Bulk density, g cm−3 1.34 1.25 1.22 1.27 1.32
± ± ± ± ±
0.05 0.02 0.05 0.08 0.07
Carbon, g 100 g−1
Bulk density, g cm−3
−5 −1 −6 −10 −12
+2 −4 −8 −5 −1
<0.001
Fig. 5. Comparison of the mean yields of all cultivars and mixtures across years and treatments. LSD = 0.351.
Fig. 7. Changes in the yield of the four cultivars and their mixture overall across the years. LSD = 0.210.
cultivars (Fig. 6). This was also seen in the trend across the years as Pastoral was the best performing cultivar in 2008 when the soil tillage treatment differences were longest established and it became the highest yielding cultivar (Fig. 7). In contrast, Fanfare shows a declining trend in its performance from being one of the highest yielding cultivar to the lowest under zero tillage, and low under minimal tillage too (Fig. 8). Sumo performed best overall under deep plough conditions, whereas Pipkin was the best cultivar under conventional and zero tillage conditions (Fig. 6). However, these are only relative trends, not statistically significant differences, and the mixture of all four cultivars was more consistent than the yield of individual monocultures. The cultivars were grouped into monocultures, 2-component (simple) mixtures, and the 3-component and the 4-component (complex) mixtures together for further analysis. Comparing
years 2004, 2005, 2007 and 2008, overall both the simple and complex sets of mixtures appeared to give higher yields than the monocultures, with the complex mixtures generally showing greatest yield (Table 4). However, the mean yields across all the years for the 2-component mixtures, and for the 3- and 4-component mixtures together, were not significantly different when compared with the monoculture mean using a contrast and their standard error (Snedecor and Cochran, 1980). Performance varied in different years and differences were small under low nitrogen conditions but comparing 2004, 2005, 2007 and 2008 under standard nitrogen the differences were much more obvious, as were the effects of changing soil treatments. In 2004 and 2005 the monocultures gave consistently lower yields than the mixtures for all treatments, around 3% for the simple mixtures and 4% for
Fig. 6. Percentage yield difference of the four cultivars and their 4-component mixture under different soil disturbance treatments compared with the overall mean yield (excluding 2006).
Fig. 8. Changes in the yield of the four cultivars and their 4-component mixture between 2004 and 2008 in response to soil tillage conditions. LSD = 0.402.
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Table 3 Rhynchosporium area under the disease progress curve (AUDPC) values for each season average and each cultivar–nitrogen average.
N1 N2
2004 59.64 Fanfare 4.08 10.83
2005 46.27 Pastoral 3.90 6.88
2006 15.85 Pipkin 46.81 227.13
2007 9.12 Sumo 6.41 74.42
2008 12.52
2008 score was N2 only. LSD years = 16.62; cultivars × nitrogen = 9.90.
Fig. 9. Comparison of rhynchosporium infection each year on different tillage treatments.
the complex mixtures. However, in 2007 and 2008 the benefits of mixtures were not apparent (−0.7 and 0.4%). The monocultures have significantly different yields and disease resistances and contribute their characteristics in different ways to the mixtures. Beneficial yield responses were generally most evident with cultivars most susceptible to disease - Pastoral and Pipkin; and in the most complex 4-component mixture. However, as the overall mixture effects were small, individual mixture comparisons would not be expected to show significant differences. Thousand grain weight data followed a similar trend to yield, again with few significant differences but a trend towards better weights in the better yielding, more disturbed soil conditions. 3.5. Disease The most common disease was rhynchosporium which was scored in all years. Its severity varied through the season tending to be slightly greater in zero tillage than the other soil treatments early in the season (data not shown). However, differences were inconsistent so Area Under the Disease Progress Curve (AUDPC) scores were analysed as the best reflection of overall damage caused to the crop. In 2004 this comprised four scores, five in 2005, three in 2006, two in 2007 and three in 2008. In 2004 and 2005 rhynchosporium mean scores appeared lowest on deep plough and highest on zero (2004) or minimum (2005) (Fig. 9). A similar pattern was found in 2006 but it was not possible to make reliable comparisons because of big differences in crop densities affecting disease development (data not shown). In 2007 the zero and minimum treatments again had the highest rhynchosporium levels but in 2008 they were the lowest. Mildew occurred at low levels in all years and was only at sufficient severity to be scored in 2006 when it was scored twice. It was greatest in the deep plough treatment, significantly more than the zero and minimum tillage treatments, but this probably reflects nutrient availability differences between treatments due to crop density effects from poor winter survival as such biotrophic pathogens are generally responsive to nitrogen levels. These data are therefore of little use and are not considered further. Raw data were square-root transformed to improve residual distributions. As with yield, nitrogen, cultivar and year were highly significant, as were many interactions. However, soil tillage treatment was clearly not significant, but interaction with year and cultivar was. There was more than five times the rhynchosporium severity in the standard nitrogen treatment compared with the low nitrogen (Table 3). There was also more than four times the rhynchosporium infection in the first two years compared with the subsequent three. Rhynchosporium was disproportionately increased in the more susceptible cultivars, namely Pipkin and Sumo.
Fig. 10. Comparison of the effect of mixtures of different complexity for controlling rhynchosporium under different soil disturbance conditions across all years.
The grouped monoculture and mixture contrasts show most mixtures decreased rhynchosporium in all years and tillage conditions. The means indicate the magnitude of these reductions, ranging from 48 to 77%, the complex mixtures generally being around 32% better than the simple mixtures (Fig. 10). The mean rhynchosporium AUDPC across all the years for the 2-component mixtures, and for the 3- and 4-component mixtures together, was compared with the monoculture mean using a contrast and its standard error (Snedecor and Cochran, 1980) and was found to be always highly significantly different (p < 0.001). There was a trend towards less difference in the minimum and zero tillage treatments (Table 4 and Fig. 11). The reduction in disease was similar in high and low nitrogen treatments overall. As with yield, under standard nitrogen infection in 2004 and 2005 behaved differently from the more mature treatments in 2007 and 2008. In 2007 and 2008 the mixtures always had less infection than the monocultures but some
Fig. 11. Rhynchosporium in mixtures and monocultures showing correlation between disease severity and effect.
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Table 4 Comparison of the effect of mixtures on rhynchosporium levels and yield in barley cultivar mixtures of different complexity under different soil disturbance conditions. Compact
Conventional
AUDPC Monoculture 49.74 2-component 19.16 3- & 4-comp. 11.33 Mean 24.71 LSD (0.05) of means = 8.64 Percentage disease reduction cf. monoculture 61% 2-component 77% 3- & 4-component Yield Monoculture 2-component 3- & 4-component Mean LSD (0.05) of means = 0.26 Percentage yield increase cf. monoculture 2-component 3- & 4-component
Deep
Minimum
Zero
46.60 18.97 12.28 24.11
43.55 15.03 9.69 20.86
48.92 25.29 19.72 29.73
48.98 21.33 15.34 26.71
59% 74%
65% 78%
48% 59%
56% 68%
2.96 2.97 3.01 2.98
3.08 3.11 3.12 3.11
3.05 3.10 3.09 3.08
2.96 2.93 2.99 2.96
2.69 2.76 2.77 2.74
0.3% 1.7%
1.0% 1.3%
1.6% 1.3%
−1.0% 1.0%
2.6% 3.0%
were not significantly different (Fig. 11). However, disease values were much lower in 2007 and 2008 as there were fewer epidemic cycles (Fig. 10). 4. Discussion Cultivar-specific effects of soil cultivation practices were observed on the yield of barley crops over a five year period. Whilst the average yields under high soil disturbance conditions tended to increase from 2004 to 2008, the opposite was observed under zero tillage, resulting in a 20% drop in yield over the same time (Fig. 5). The traditional breeding approach that relies on highly favourable growing conditions may therefore not identify lines that perform better under reduced tillage. All cultivars yielded similarly in response to all soil disturbance treatments but Pastoral was affected most, showing a greater response to minimum tillage treatment but not responding as well as the other cultivars to deep plough conditions. Differences in rankings reflecting these responses increased as the soil conditions developed across the years, Pastoral going from the lowest to the highest yielding cultivar and Fanfare doing the opposite between 2004 and 2008 data. There was little effect on thousand grain weight for any treatment and nitrogen treatment had only effects on the scale of responses (Table 5). Rhynchosporium was a major disease in this trial, mostly in the earlier years. Mildew was recorded at significant levels in the problematic 2006 trial but no disease was recorded at levels likely to affect yield to a great extent in 2006, 2007 or 2008. Rhynchosporium severity was greatest in the standard nitrogen treatments and in the more susceptible cultivars, but again there was no interaction with soil tillage treatment. There was a suggestion in the data that under zero tillage rhynchosporium was more severe early season, or conversely that treatments such as deep plough minimised early season infection, and this would be expected as it would correlate with the amount of crop debris with inoculum (Atkins et al., 2010). In all years except 2008 either or both the minimum and zero tillage treatments had more rhynchosporium overall, but in 2008 the opposite occurred. This may be a reflection
of an equilibrium being established between pathogens and their antagonists as found for eyespot in wheat (Kuntzsch, 1990; Jamaluddin and Jenkyn, 1996; Burnett and Hughes, 2004). Under the different tillage treatments, the distribution of residue, soil physical conditions and weed seed propagation will influence yield responses (George et al., 2009; Arvidsson, 1998). Furthermore, penetrometer resistance >2 MPa is likely to at least halve root elongation rate (Bengough, 1997) and the depth at which this occurred varied between 180 mm and 280 mm in the minimum and deep plough tillage treatments respectively. Before these conditions are discussed, however, it needs to be emphasised that the study was conducted in a temperate, maritime climate. Whereas many studies internationally have demonstrated the benefits of reduced tillage compared to ploughing for carbon (Lal, 2009), biota and physical conditions in soil (Govaerts et al., 2007), the local conditions of this study resulted in dense surface soil and shallow plough or traffic pans developing (personal communication. Bruce Ball, SAC, Edinburgh). Under deep plough, however, this will be off-set by roots accessing water at greater depth (McKenzie et al., 2009). The compaction treatment increased mechanical impedance to rooting and this could explain the small drop in yield compared to ploughing and deep ploughing in some years of the experiment (Bengough, 1997; Atkinson et al., 2007). There were distinct differences in penetration resistance with depth between treatments that reflect the observed changes in yields. With improved traffic guidance systems, opportunities are emerging for controlled traffic to prevent soil compaction occurring in large proportions of cereal fields. Preventing the creation of dense pans in the soil may provide opportunities to reduce tillage under the climatic conditions found here. A major trait used to select the four cultivars grown in this experiment was the root morphology of seedlings. Pipkin seedlings had the longest root length (Fig. 3) and had the smallest yield reduction under zero tillage of all cultivars (Fig. 6), whereas Pastoral seedlings had the shortest root length and had the greatest yield penalty. This cultivar may therefore establish a deeper root system in the field over the winter and spring when soil water contents are large enough for penetration resistance to not limit root elongation. The
Table 5 Mean yields across years and treatments (kg/plot). Year
2004 2.975
2005 3.279
2006 2.450
2007 3.052
2008 3.110
LSD 0.028
Treatment
Compact 2.977
Conventional 3.104
Deep 3.081
Minimum 2.962
Zero 2.742
LSD 0.028
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different cultivars may also have different morphological plasticity of roots in response to soil physical conditions (Bingham and Bengough, 2003). Current research is investigating the response of roots of different cultivars to soil physical conditions in this field experiment. By planting mixtures, increased resilience was evident from smaller shifts in yields between cultivation treatments and growing seasons. Mixtures enhanced yield in 2004 and 2005 in proportion to their complexity as expected from previous data (Newton et al., 1997) but differences were small or not significant in 2007 and 2008. There was no interaction with soil tillage condition in the efficacy of the mixtures on yield or thousand grain weight. As for yield, mixtures had a much more pronounced effect on rhynchosporium infection in 2004 and 2005 compared with the other years, and in 2008 they had no effect, probably a reflection of the very low disease levels in the latter years. As mixtures reduce disease by extending the epidemic cycle length, with few cycles they will have little effect. However, mixtures reduced infection substantially and in similar amounts in proportion to their complexity across all tillage treatments, but showed a tendency towards improved efficacy on minimum and zero tillage treatments. As well as contrasting root and disease resistance traits, cultivars differed in agronomic traits, particularly yield sensitivity. This measures cultivar differential yield responses to soil conditions or site fertility. In the UK Variety Recommended List trial system (hgca.com) this was calculated by determining the relative yields of a panel of cultivars on sites with differing yield potentials, namely 5, 7 and 9 tonnes per hectare, across several consecutive seasons. Yield sensitivity where values greater than 1.0 indicate that a cultivar is more sensitive to changes in site yield/fertility, i.e. it is better able to respond to high yielding conditions. Conversely, a low sensitivity cultivar is likely to perform relatively well on low yield potential sites (NIAB, 2001; Finlay and Wilkinson, 1963). The selected cultivars ranged from 0.80 for Pipkin to 1.06 for Sumo, these being the best yielding cultivars under deep plough and zero tillage treatments respectively (Fig. 6). Thus yield sensitivity may also correlate with degree of soil disturbance presumably making nutrients more available and thereby a proxy for yield potential. The hypothesis that using cultivars complementary in root traits would mimic below ground the complementarity of heterogeneous traits above ground (Newton et al., 2009), was not demonstrated in this work. Some cultivar combinations may have suited particular soil treatments, but if so then the advantages were small and not expressed by their effect on the means. However, the cultivars were selected on seedling root differences and although some interactions between monocultures and soil conditions were found, the differences were not great and therefore the potential complementarity effects may have been small. Selection based on adult plants roots might have been better, but as all roots are highly responsive to soil environments (Passioura, 1991), gross differences may still not have been enough to see significant interactions. A subsequent preliminary screen of many more cultivars has identified ones with strong differential interactions with low and high soil disturbance conditions (Newton, Bengough et al., unpublished data). Unfortunately, the cultivars used in the work reported here were amongst the ones that showed relatively little differential response. Overall we show some differential cultivar response to soil tillage conditions, a buffering of this difference in mixtures, and a benefit of using mixtures expressed in both yield response and disease control under all soil tillage conditions. We have indications that looking at a much wider range of barley genotypes might reveal stronger interactions with soil tillage. If such genotypes can be identified then they may still best be deployed in mixtures as soil conditions are highly variable between seasons, and mixtures enable responsive cultivars to be always in situ to best utilise available resources.
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Acknowledgements We thank the Scottish Government Rural and Environment Science and Analytical Services (RESAS) for funding from the Sustainable Agriculture - Plants programme. We thank Christine Hackett of Biomathematics and Statistics Scotland (BioSS) for statistical advice and analysis. We also thank the farm staff at the Invergowrie site of the James Hutton Institute. References Arvidsson, J., 1998. Effects of cultivation depth in reduced tillage on soil physical properties, crop yield and plant pathogens. Eur. J. Agron. 9, 79–85. Atkinson, B.S., Sparkes, D.L., Mooney, S.J., 2007. Using selected soil physical properties of seedbeds to predict crop establishment. Soil Till. Res. 97, 218–228. Bengough, A.G., 1997. Modelling rooting depth and soil strength in a drying soil profile. J. Theor. Biol. 186, 327–338. Bengough, A.G., Gordon, D.C., Al-Menaie, H., Ellis, R.P., Allan, D., Keith, R., Thomas, W.T.B., Forster, B.P., 2004. Gel observation chamber for rapid screening of root traits in cereal seedlings. Plant Soil 262, 63–70. Betz, C.L., Allmaras, R.R., Copeland, S.M., Randall, G.W., 1998. Least limiting water range: Traffic and long-term tillage influences in a Webster soil. Soil Sci. Soc. Am. J. 62, 1384–1393. Bell, J.S., Hipkin, J.A., 1988. Soils of Mylnefield and Gourdie farms, Scottish Crop Research Institute. Macaulay Land Use Research Institute, Aberdeen. Bingham, I.J., Bengough, A.G., 2003. Morphological plasticity of wheat and barley roots in response to spatial variation in soil strength. Plant Soil 250, 273–282. Burnett, F.J., Hughes, G., 2004. The development of a risk assessment method to identify wheat crops at risk from eyespot. HGCA Project report number 347. Home-Grown Cereals Authority, London, 91 pp. Brooks, D.H., Dawson, M.G., 1968. Influence of direct-drilling of winter wheat on incidence of take-all and eyespot. Ann. Appl. Biol. 61, 57–64. Finckh, M.R., Gacek, E.S., Goyeau, H., Lannou, C., Merz, U., Mundt, C.C., Munk, L., Nadziak, J., Newton, A.C., de Vallavieille-Pope, C., Wolfe, M.S., 2000. Cereal variety and species mixtures in practice, with emphasis on disease resistance. Agronomie 20, 813–837. Finlay, K.W., Wilkinson, G.N., 1963. The analysis of adaptation in a plant breeding programme. Aust. J. Agric. Res. 14, 742–754. Govaerts, B., Fuentes, M., Mezzalama, M., Nicol, J.M., Deckers, J., Etchevers, J.D., Figueroa-Sandoval, B., Sayre, K.D., 2007. Infiltration, soil moisture, root rot and nematode populations after 12 years of different tillage, residue and crop rotation managements. Soil Till. Res. 94, 209–219. HGCA, 1999. UK Recommend List of cereals, cereals variety handbook 1999. HGCA, 144 pp. HGCA, 2001. UK Recommend List of cereals, cereals variety handbook 2001. HGCA, 160 pp. Jaeger, M.J., Jones, D.G., Griffiths, E., 1981. Disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars. II. Experiments. Ann. Appl. Biol. 98, 187–198. Mundt, C.C., 2002. Use of multiline cultivars and cultivar mixtures for disease management. Annu. Rev. Phytopathol. 40, 381–410. Jamaluddin, M., Jenkyn, J.F., 1996. Effects of wheat crop debris on the sporulation and survival of Pseudocercosporella herpotrichoides. Plant Pathol. 45, 1052–1064. Kuntzsch, E., 1990. Yield, yield components and infection with Pseudocercosporella herpotrichoides during long-term winter wheat monoculture in the Etzdorf teaching and research station 1972-1987. Wissenschaftliche Zeitschrift MartinLuther-Universitaet Halle-Wittenberg Mathematisch-Naturwissenschaftliche Reihe 39, 107–113. Lal, R., 2009. Challenges and opportunities in soil organic matter research. Eur. J. Soil Sci. 60, 158–169. McKenzie, B.M., Bengough, A.G., Hallett, P.D., Thomas, W.T.B., Forster, B., McNicol, J.W., 2009. Deep rooting and drought screening of cereal crops: a novel fieldbased method and its application. Field Crops Res. 112, 165–171. Melero, S., Lopez-Garrida, R., Madejon, E., Murillo, J.M., Vanderlinden, K., Ordonez, R., Moreno, F., 2009. Long-term effects of conservation tillage on organic fractions in two soils in southwest of Spain. Agric. Ecosyst. Environ. 133, 68–74. Montanari, M., Innocenti, G., Toderi, G., 2006. Effects of cultural management on the foot and root disease complex of durum wheat. J. Plant Pathol. 88, 149–156. Newton, A.C., Hackett, C.A., 1994. Subjective components of mildew assessment on spring barley. Eur. J. Plant Pathol. 100, 395–412. Newton, A.C., Ellis, R.P., Hackett, C.A., Guy, D.C., 1997. The effect of component number on Rhynchosporium secalis infection and yield in mixtures of winter barley cultivars. Plant Pathol. 46, 930–938. Newton, A.C., Guy, D.C., 2008. The effects of uneven, patchy cultivar mixtures on disease control and yield in winter barley. Field Crops Res. 110, 225–228. Newton, A.C., Hackett, C.A., Swanston, J.S., 2008a. Analysing the contribution of component cultivars and cultivar combinations to malting quality, yield and disease in complex mixtures. J. Sci. Food Agric. 88, 2142–2152. Newton, A.C., Swanston, J.S., Guy, D., Hallett, P.D., 2008b. Variety mixtures: on farm mixing and interaction with cultivation methods. In: Proceedings of the Crop Protection in Northern Britain Conference, 2008, pp. 115–212. Newton, A.C., Begg, G., Swanston, J.S., 2009. Deployment of diversity for enhanced crop function. Ann. Appl. Biol. 154, 309–322.
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NIAB, 2001. UK Recommended List of Cereals; 2001 cereal variety handbook. NIAB, Cambridge. Olsen, C.C., Hovmøller, M.S., Henneberg, U., Stølen, O., Welling, B., 1986. Cultivar mixtures of winter barley 1983-85. Meddelelse, Statens Planteavlsforsog 88, 4 pp. Passioura, J.B., 1991. Soil structure and plant-growth. Aust. J. Soil Res. 29, 717–728. Rasmussen, K.J., 1988. Ploughing direct drilling and reduced cultivation for cereals. Tidsskr. Planteavl 92, 233–248. Rieger, S., Richner, W., Streit, B., Frossard, E., Liedgens, M., 2008. Growth, yield and yield components of winter wheat and the effects of tillage intensity, preceding crops, and N fertilization. Eur. J. Agron. 28, 405–411. Riley, H.C.F., Bleken, M.A., Abrahamsen, S., Bergjord, A.K., Bakken, A.K., 2005. Effects of alternative tillage systems on soil quality and yield of spring cereals on silty clay loam and sandy loam soils in the cool, wet climate of central Norway. Soil Till. Res. 80, 79–93. Snedecor, G.W., Cochran, W.G., 1980. Statistical Methods, Seventh edition, Iowa State University Press, Ames, Iowa, USA, 507 pp. Townwend, T., Reeve, M.J., Carter, A., 2001. Water release characteristic. In: Smith, K.A. Mullins, C.E. (Eds.), Soil and Environmental Analysis Physical Methods, Second Edition, Marcel Dekker New York, pp. 95–140.
Turkington, T.K., Xi, K., Clayton, G.W., Burnett, P.A., Klein-Gebbinck, H.W., Lupwayi, N.Z., Harker, K.N., O’Donovan, J.T., 2006. Impact of crop management on leaf diseases in Alberta barley fields, 1995-1997. Can. J. Plant Pathol. 28, 441–449. Verch, G., Kachele, H., Holtl, K., Richter, C., Fuchs, C., 2009. Comparing the profitability of tillage methods in Northeast Germany-A field trial from 2002 to 2005. Soil Till. Res. 104, 16–21. Wang, W.J., Dalal, R.C., 2006. Carbon inventory for a cereal cropping system under contrasting tillage, nitrogen fertilisation and stubble management practices. Soil Till. Res. 91, 68–74. Wolfe, M.S., 1985. The current status and prospects of multiline cultivars and variety mixtures for disease resistance. Annu. Rev. Phytopathol. 23, 251–273. Yarham, D.J., 1975. The effect of non-ploughing on cereal diseases. Outlook Agric. 8, 245–247. Yarham, D.J., Norton, J., 1981. Effects of cultivation methods on disease. In: Jenkyn, J.F., Plumb, R.T. (Eds.), Strategies for the Control of Cereal Disease. Blackwell Scientific Publications, Oxford, UK, pp. 157–166.
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Soil tillage effects on the efficacy of cultivars and their mixtures in winter barley A.C. Newton a,∗ , D.C. Guy a , A.G. Bengough a,b , D.C. Gordon a , B.M. McKenzie a , B. Sun a , T.A. Valentine a , P.D. Hallett a a b
The James Hutton Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK Division of Civil Engineering, University of Dundee, Dundee DD1 4HN, UK
a r t i c l e
i n f o
Article history: Received 5 August 2011 Received in revised form 9 December 2011 Accepted 13 December 2011 Keywords: Blends Cultivation Mildew Rhynchosporium Disease Yield
a b s t r a c t Cereal farming is moving rapidly towards reduced tillage, with over 100 million ha of land currently tilled using minimum tillage implements. This study reports five years of data from a field experiment investigating the response of different barley cultivars and mixtures to soil tillage practice and nitrogen fertiliser levels. Five tillage treatments were established that imposed different amounts of soil disturbance: (T1) zero tillage, (T2) minimum tillage to 7 cm depth and ploughed treatments followed by power harrowing consisting of (T3) conventional plough to 20 cm depth, (T4) plough to 20 cm followed by compaction by wheeling the entire plot with a tractor fitted with 8.8 Mg total load and (T5) deep plough to 40 cm depth, all on the same site each year. Four winter barley cultivars (Sumo, Fanfare, Pastoral and Pipkin) were selected based on contrasting rooting characteristics, disease resistance and yield sensitivity. They were planted in plots as monocultures and as all 2-, 3- and 4-component mixtures thereof. Significant differences in soil physical properties and carbon content were observed over the five years of the study. Grain yield varied by 13% between tillage treatments, with conventional and deep plough conditions generally the highest yielding and zero tillage the lowest. Sumo gave the highest yield overall under deep plough conditions, whereas Pipkin was the best cultivar under conventional and zero tillage conditions. Rhynchosporium was the most common disease and the mixture gave decreased infection in all years and tillage conditions. Complex mixtures gave around 32% less disease than the simple mixtures. There was an overall differential cultivar response to soil tillage conditions that was buffered by cultivar mixtures. Mixtures offered benefits in both yield response and disease control under all soil tillage conditions. © 2011 Elsevier B.V. All rights reserved.
1. Introduction There have been several comparisons of yield performance of cereals under different tillage regimes and disease incidence has been monitored for some of these (e.g. Riley et al., 2005; Melero et al., 2009). Such research is vital to understanding crop responses to evolving farming practices, as the large shift towards conservation tillage in semi-arid climates has not occurred to the same extent in the cool and humid areas of Europe. Rieger et al. (2008) attributed this slower adoption to a lack of knowledge about agronomic and ecological impacts. Most European breeding trials are based on soils cultivated to at least 20 cm depth with a pass from both plough and harrow, whereas over 100 million ha of farmland is tilled using single pass minimum tillage implements to <10 cm or direct-drilling (Verch et al., 2009). Less intense tillage can have a large impact on the root environment, particularly mechanical impedance, aeration and plant available water in soil (Betz et al.,
∗ Corresponding author. Tel.: +44 1382 568824. E-mail address: [email protected] (A.C. Newton). 0378-4290/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.fcr.2011.12.004
1998). Plant traits that respond well to these conditions may be different from those selected in breeding trials using intensive tillage. For instance, reduced tillage preserves continuous macro- and biopores in soil, which some cereal cultivars may exploit better than others (McKenzie et al., 2009). Another major difference between ploughing and reduced tillage is the distribution of plant debris on the soil surface and in the topsoil (Wang and Dalal, 2006). Plant root growth is likely to be affected greatly by differences in soil physical conditions such as compaction, plough pans and continuity of macro- and micro-pores. High soil disturbance will enable roots to access water at greater depth for example (McKenzie et al., 2009). Compaction will increase mechanical impedance to rooting (Bengough, 1997; Atkinson et al., 2007). Therefore differences between cultivars in their root morphological traits such as their length, depth and angle might result in differential performance under different tillage treatments. The advantages of cultivar mixtures in minimising disease and increasing yield compared with the mean of their monocultures, and providing yield stability, are well established (Finckh et al., 2000; Wolfe, 1985; Mundt, 2002; Newton et al., 2009). The disease control trait is particularly advantageous where zero or low
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use of synthetic pesticides is permitted such as in organic or low input systems respectively. Much of the published data on mixtures of cereals is from various conventional farming systems characterised by intensive soil tillage by ploughing and high levels of synthetic inputs. Given shifts towards reduced tillage and fertiliser use, enhanced crop function may be required and may be achieved through deployment of diversity, and specifically through the use of cultivar mixtures (Newton et al., 2009). In general, where plant debris is the source of inoculum, burying it by ploughing reduces foliar diseases (Montanari et al., 2006; Yarham, 1975). However, in other reports disease incidence was independent of tillage methods (Rasmussen, 1988), probably because the effects of previous crops and their disease incidence and severity was greater (Turkington et al., 2006). This demonstrated the increased importance of crop rotation, particularly in reduced tillage situations (Arvidsson, 1998). The severity of eyespot (Oculimacula yallundae) under minimum versus conventional tillage conditions has been observed to decrease over successive minimum tillage seasons (Brooks and Dawson, 1968) and whilst this is partly explained by differences in plant habit under the different cultivation conditions (Yarham and Norton, 1981) it may also be due to establishment of an equilibrium between pathogens and their antagonists (Kuntzsch, 1990; Jamaluddin and Jenkyn, 1996; Burnett and Hughes, 2004). The incidence of rhynchosporium caused by Rhynchosporium secalis infection on barley is clearly increased by reduced cultivation as crop debris from previous crops is not buried (Turkington et al., 2006; Arvidsson, 1998; Yarham, 1975). Growing barley in mixtures has been shown to decrease rhynchosporium severity (Jaeger et al., 1981; Horoszkiewicz-Janka and Michalski, 2003; Olsen et al., 1986; Newton et al., 1997, 2008a, 2008b; Newton and Guy, 2008). However, the relative performance of cultivar mixtures under different tillage regimes has been determined for neither yield nor disease control traits. Nor is it known whether the severity of R. secalis infection changes as inoculum and any antagonists establish in reduced tillage systems across successive years. Most mechanistic studies of cultivar mixtures have concerned the aerial environment and foliar pathogens. Whilst this is appropriate for epidemiological studies of leaf pathogens, particularly if the soil surface debris and its environment are taken into consideration, for yield studies resource capture above ground is clearly only a part of the crop production system. Efficiency of water and nutrient capture from the soil may be a critical component of differences between cultivars, and interactions between different rooting strategies a key to understanding overall mixtures performance. Therefore cultivars with different rooting characteristics need to be assessed individually and in interactions, and contrasting root environments such as those created by different cultivation regimes should be used to vary the potential for expressing the benefits of these different characteristics. This paper reports five years of data from a field investigation of the response of barley cultivars with contrasting root, disease resistance and other agronomic traits, grown singly and in mixtures, to soil tillage practice and nitrogen fertiliser levels. There were five soil tillage practices used, which cultivated soil to a range of depths from 0 cm (no-till) to 40 cm (deep plough). One ploughed treatment was also compacted by wheeling. This produced differences in the soil environment experienced by crop roots, thereby enabling study of the genotype × environment interactions of a range of barley lines and mixtures thereof. We hypothesised that cultivars would differ in their response to tillage treatments and that the mixtures would confer greater resilience to changes in tillage practice, resulting in greater and more stable yield under shallow cultivation. The cultivar response differences might be correlated with root trait differences and the mixtures advantage might be attributable to a combination of enhanced resistance to disease spread and
increased tolerance of soil conditions from complementarity of contrasting root traits. 2. Materials and methods 2.1. Root and shoot characteristics Based on the UK Recommended List of Cereals (hgca.com) published variety characteristics of height, standing power, earliness, yield sensitivity, powdery mildew resistance and rhynchosporium resistance, cultivars were selected with contrasting traits. These were characterised for total seedling root length, average longest root, average shoot length, and average root angular spread using a gel observation chamber described by Bengough et al. (2004). It consisted of 2 mm thick layers of water agar on flat sheets, 300 mm height by 215 mm width that were separated by a 2 mm thick airgap when placed together. Roots were grown in the gap and a Perspex front face allowed observation of the roots. After 10 days the chambers were scanned at a resolution 800 dpi and the root characteristics were analysed with Scion image software. Using all these traits, but with an emphasis on root traits, four cultivars were selected for contrasting traits (Fig. 3 and Table 1), namely Fanfare, Pastoral, Pipkin and Sumo. 2.2. Soil characteristics Soil conditions were manipulated in a field experiment by using different forms of tillage. The soil was a Dystric-Fluvic Cambisol with a sandy-loam surface texture (Bell and Hipkin, 1988). It had a pH of 5.7, was freely drained and underlain by colluvial sand at 60 cm depth. To minimise in-field variability the entire site was first uniformly ploughed to 20 cm, power harrowed and sown with the spring barley variety (var. Optic) in spring 2003 (year 0). Auger holes were dug to 50 cm at 20 random locations across the experiment site to observe depth of the plough layer (Ap), plough pans and the nature of the subsoil sediment. In July, baseline measurements of soil carbon and nitrogen were determined on samples taken at 0–10 cm depth on a 4 × 4 evenly spaced grid that covered the entire experimental field. At each point on the grid, sampling was done at five nearby locations and then mixed. Soils were dried at 105 ◦ C, ball-milled and then measured using a continuous flow mass spectrophotometer consisting of an ANCA SL sample converter attached to a 20-20 IRMS (Europa Scientific, Crewe, UK) in 2003 and 2004, and with an Exeter Analytical CE440 Elemental Analyzer (EAI, Coventry, UK) in 2008. Prior to harvest, blocks corresponding to the subsequent experiment layout shown in Fig. 1 were marked out and the barley was harvested from each block to approximate yield and the evenness of the site. 2.3. Treatments and trial design Five tillage treatments were established in autumn 2003 that imposed different levels of soil disturbance: (T1) zero tillage, (T2) minimum tillage to 7 cm depth and ploughed treatments followed by power harrowing consisting of (T3) conventional plough to 20 cm depth, (T4) plough to 20 cm followed by compaction by wheeling the entire plot with a Massey Ferguson 6270 tractor fitted with 16.9R-38 rear tyres (8.8 Mg total load, 2.9 Mg wheel load and 110 kPa contact pressure) and (T5) deep plough to 40 cm depth. These treatments were selected to provide different physical constraints to root growth and water availability. Fifteen blocks each 33 × 33 m were marked out in an even grid with five blocks in each of three north-south columns representing the three treatment replicates. Blocks were separated from each other by strips at least 3 m wide that were sown with grass seed after the first trial year was sown (Fig. 1).
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Fig. 1. Layout of soil tillage treatments 2003–2008 and the yield (kg) of spring barley in year 0 prior to treatments being applied.
Within each of the 15 blocks, a split block trial was sown. There were 15 trial entries comprising the four monocultures, all six 2component, all four 3-component and the 4-component mixture in equal proportions adjusted by thousand grain weights (Table 1). Plots measured 1.55 m wide × 6.0 m long, reduced to 4.8 m harvested length by plot definition, and were sown at 360 seed/m2 with an eight-row Hege plot drill with five plots per bed. Three replicates and two fertiliser levels were used, N1 = half rate and N2 full rate 180 kgN/ha, P, K) applied as top dressings in April and again in May (Fig. 2). In 2008 the N1 treatment was discontinued
but the N2 (full rate) was sown as before. The trial was sown in five successive years and whilst the randomisations were different for every block, identical randomisations were used each year so that the same monoculture or mixture was sown in the same place every year. No fungicide treatments were applied to the plots. Each year all plots were harvested when ripe using a Wintersteiger plot combine, and the grain was dried to constant moisture and weighed. In 2004, 2005, 2006 and 2008 the thousand grain weights were assessed. Straw was removed from all of the plots following harvest.
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Table 1 Characteristics of winter barley varieties selected for mixtures trialling. Cultivars/mixtures
Agronomy
Disease resistance
Yield
Shortness
Standing
Earliness
Rhynchosporium
Mildew
Sensitivity
Sumo Fanfare Pastoral Pipkin
7a 7 7 7
7a 5 7 4
5a 5 6 5
5a 8 8 3
6a 5 5 2
1.06b 0.84 0.97 0.80
2 component mixtures (6): 3-component mixtures (4): 4-component mixture (1):
Sumo-Fanfare, Sumo-Pastoral, Sumo-Pipkin, Fanfare-Pastoral, Fanfare-Pipkin, Pastoral-Pipkin Sumo-Fanfare-Pastoral, Sumo-Fanfare-Pipkin, Sumo-Pastoral-Pipkin, Fanfare-Pastoral-Pipkin Sumo-Fanfare-Pastoral-Pipkin
a b
Strength of trait expression on a 1 (low) to 9 (high) scale. HGCA UK Recommended Lists for cereals: Cereal variety handbook (HGCA, 1999, 2001). Above 1 = cultivar more sensitive than average to changes in site yield; below 1 = cultivar has below average response to changes in site yield (HGCA, 1999, 2001).
2.4. Assessments and analysis Diseases were scored on a 1-9 whole plant severity scale (Newton and Hackett, 1994) when above trace levels, and scored again at approximately two-weekly intervals. Scores were converted to percentage infection and the Area Under the Disease Progress Curve (AUDPC) calculated. At the beginning of the first growing season in April 2004 and the end of the final growing season in October 2008, 56 mm diameter × 40 mm height soil cores were sampled from 2 to 7 cm depth at 3 random locations in each experimental block to determine soil dry bulk density. Soil water release was measured as a function of soil matric potential for these soil samples using a tension table and pressure plate apparatus (Townwend et al., 2001). Plant available water content was determined as the difference between volumetric water content at a matric potential of −1.5 MPa (wilting point) and at −0.5 kPa (field capacity). Disturbed soil samples were collected from the same locations from 0 to 10 cm for carbon measurements. pH was measured on a 1:5 soil:water mix. Penetration resistance was measured at three random locations in each block at the start of the first growing season. Measurements were done to a depth of 40 cm at 2 cm
N1
N2
N1
N2
Guard T-rep 1
T-rep 2
Guard 2
N2
Guard
N1
T-rep 3
Fig. 2. Treatment design within a replicate block. T-rep = replicate within a treatment and block. Guard = Sumo. Guard 2 = Pastoral. Trial entry plots: 1350 in total, 450 within a replicate block.
increments using a Rimik Cone Penetrometer (Rimik, Toowoomba, Australia). Analysis of variance was carried out using Genstat eleventh edition for Windows (VSN International Ltd, Hemel Hemstead, UK) using a split-split plot model with tillage treatment as the main plot, nitrogen as the sub-plot, and cultivar as the sub-sub-plot. A set of contrasts were set up to test monoculture compared with mixtures effects where required (Newton et al., 2008a). For comparing mixtures, the cultivars were grouped into monocultures, 2-component (simple) mixtures, and the 3-component and the 4component (complex) mixtures together for further analysis. These were analysed using analysis of variance and series of contrasts were calculated from the variety means to test the significance of particular comparisons, such as monocultures versus 2-component mixtures, balanced so that each variety had equal weight in all comparisons. 3. Results 3.1. Experimental site and seasons The area of land chosen for this experiment shown in Fig. 1 illustrates unevenness in crop yield from west to east, highlighted by how different replicate 3 was from replicates 1 and 2 in yield of the year 0 spring barley crop, a difference of around 10% that was significant when treated as a factor (p = 0.003). However, there were no significant differences (p = 0.646) between the areas chosen for the five treatments overall, the mean yields differing by only 36 kg (LSD = 55 kg), illustrating the utility of the randomisation in the treatment design. The baseline soil data for water content (14.3 ± 1.4 g 100 g−1 s.e.), carbon (2.5 ± 0.03 g 100 g−1 s.e.) and nitrogen (0.2 ± 0.01 g 100 g−1 s.e.) were similar across the experimental site (p > 0.10). Auger holes to 50 cm depth showed similar thicknesses of the top soil horizon (Ap). However, data from the soil survey (Bell and Hipkin, 1988) and our auger samples to 50 cm depth identified ingress of colluvial sediment in the subsoil that is more pronounced moving from east to west. A plough pan at 20–25 cm depth was observed across the entire experimental site. In 2004, 2005, 2007 and 2008 harvest years all field operations were carried out successfully. For the 2006 season it was exceptionally wet at time of sowing (data not shown) and the minimum and zero tillage treatments were the first to be accessible and were sown in early November. It was not until early December that the ground became accessible for ploughing and the other three treatments were sown. Poor establishment and subsequent winter conditions lead to severe seedling mortality, so although disease assessments and yield measurements were made and there was continuity of cropping, these data are treated differently or excluded from many analyses.
A.C. Newton et al. / Field Crops Research 128 (2012) 91–100
95
(a)
50
10
40
8 30
6 4
20
2
10
0
0
0.16 0.14
Root:Shoot Ratio
60
0.12
140 Root:Shoot
(b)
Angle
120 100
0.10
80
0.08 60
0.06 0.04
40
0.02
20
0.00
o
Length (cm)
12
Depth Length
Angle ( )
14
Total Length (cm)
70
16
0 Fanfare
Pastoral
Pipkin
Sumo
Fig. 3. Root characteristics of seedlings of the different barley cultivars after 10 days growth in a gel observation chambers. The root lengths and anglular spread were measured and the longest root length:shoot length ratio was calculated.
The root characteristics of the seedlings of the selected barley cultivars are shown in Fig. 3. Root angle and the total length of all roots were different between the cultivars (p < 0.01), but depth was similar. Stem height and hence longest root length:shoot length ratio also varied (p < 0.01), with both traits 40% greater in Sumo than Fanfare (Fig. 3). From these tests of seedlings in laboratory conditions, variable root and shoot characteristics between cultivars were identified and, together with above-ground characteristics from Recommended List data shown in Table 1 (HGCA, 1999, 2001), the four cultivars shown were selected for contrasting combinations. 3.3. Soil properties The different forms of tillage applied influenced soil physical conditions in the first year of the experiment. Penetration resistance measured in April was markedly different between plots, with deep plough having the least impedance to root growth, whereas zero and minimum tillage had greatest impedance in the topsoil and would impede root growth (resistance >2 MPa) below 180 mm (Fig. 4). By contrast the depth or impeded growth under deep plough treatment was 280 mm. On soil cores sampled from 2 to 7 cm depth at the start of the first growing season there was no difference in field capacity (25.5 ± 0.82 g 100 g−1 ) or bulk density (Table 2) between treatments (p > 0.05). Plant available water in both deep plough (13.2 ± 0.39 g 100 g−1 ) and compaction (13.4 ± 0.32 g 100 g−1 ) was about 2 g 100 g−1 less (p < 0.001) than in plough (15.2 ± 0.48 g 100 g−1 ), minimum tillage (15.2 ± 0.30 g 100 g−1 ) and zero tillage (15.9 ± 0.29 g 100 g−1 ). At the start of the experiment, soil carbon concentration was decreased under deep plough, with the effect exacerbated by the end of the experiment (Table 2).
Cultivar also showed highly significant interaction with both tillage and year (p < 0.001), and the cultivar × year × nitrogen interaction was also significant (p = 0.003). This reflected the changed behaviour between the first two establishing years and the later years of the experiment. Overall the standard nitrogen treatment increased yield by 25% over the half rate treatment, and yield varied by 13% between tillage treatments. Conventional and deep plough conditions were generally the highest yielding and zero tillage the lowest under either nitrogen treatment (Fig. 5, Table 5). However, the trend across the years was for the three high disturbance conditions to behave similarly whilst the yield from the minimum tillage decreased progressively and the yield from zero tillage decreased faster still (Fig. 5). The exception was 2006 when both low disturbance treatments yielded less than previous years but better than the high disturbance for the reasons given above. Overall, the mean yield across the years varied by only 9% excluding 2006. The four monocultures had relatively consistent yield across the different tillage treatments overall, though Pastoral appeared to yield relatively better under reduced tillage with minimum tillage ranking higher and deep plough ranking lower than with the other
0 Compacted Deep Plough Minimum Tillage Zero Tillage Plough
100
Depth (mm)
3.2. Root and shoot characteristics
200
300
400
3.4. Yield and thousand grain weight Tillage, year, nitrogen and cultivar effects on yield were highly significant overall (p < 0.001) but there were highly significant interactions between year and tillage, and year and nitrogen.
0
1
2
3
4
Penetration Resistance (MPa) Fig. 4. Penetration resistance measured in April 2004 after the first year of establishing the experiment. Error bars show +/− standard error of the means.
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Table 2 Soil characteristics at the start of the first and end of the final growing season. Tillage treatment
Year 1 (2004) Carbon, g 100 g−1
Zero tillage Min. tillage Plough Compaction Deep plough
2.79 2.84 2.72 2.88 2.56
p
0.04
± ± ± ± ±
0.08 0.10 0.04 0.08 0.06
Year 5 (2008) Bulk density, g cm−3
Carbon, g 100 g−1
1.32 ± 0.03 1.30 ± 0.02 1.32 ± 0.01 1.33 ± 0.02 1.33 ± 0.02
2.65 2.82 2.56 2.58 2.25
n.s.
<0.01
± ± ± ± ±
0.02 0.05 0.02 0.04 0.03
Percentage change Bulk density, g cm−3 1.34 1.25 1.22 1.27 1.32
± ± ± ± ±
0.05 0.02 0.05 0.08 0.07
Carbon, g 100 g−1
Bulk density, g cm−3
−5 −1 −6 −10 −12
+2 −4 −8 −5 −1
<0.001
Fig. 5. Comparison of the mean yields of all cultivars and mixtures across years and treatments. LSD = 0.351.
Fig. 7. Changes in the yield of the four cultivars and their mixture overall across the years. LSD = 0.210.
cultivars (Fig. 6). This was also seen in the trend across the years as Pastoral was the best performing cultivar in 2008 when the soil tillage treatment differences were longest established and it became the highest yielding cultivar (Fig. 7). In contrast, Fanfare shows a declining trend in its performance from being one of the highest yielding cultivar to the lowest under zero tillage, and low under minimal tillage too (Fig. 8). Sumo performed best overall under deep plough conditions, whereas Pipkin was the best cultivar under conventional and zero tillage conditions (Fig. 6). However, these are only relative trends, not statistically significant differences, and the mixture of all four cultivars was more consistent than the yield of individual monocultures. The cultivars were grouped into monocultures, 2-component (simple) mixtures, and the 3-component and the 4-component (complex) mixtures together for further analysis. Comparing
years 2004, 2005, 2007 and 2008, overall both the simple and complex sets of mixtures appeared to give higher yields than the monocultures, with the complex mixtures generally showing greatest yield (Table 4). However, the mean yields across all the years for the 2-component mixtures, and for the 3- and 4-component mixtures together, were not significantly different when compared with the monoculture mean using a contrast and their standard error (Snedecor and Cochran, 1980). Performance varied in different years and differences were small under low nitrogen conditions but comparing 2004, 2005, 2007 and 2008 under standard nitrogen the differences were much more obvious, as were the effects of changing soil treatments. In 2004 and 2005 the monocultures gave consistently lower yields than the mixtures for all treatments, around 3% for the simple mixtures and 4% for
Fig. 6. Percentage yield difference of the four cultivars and their 4-component mixture under different soil disturbance treatments compared with the overall mean yield (excluding 2006).
Fig. 8. Changes in the yield of the four cultivars and their 4-component mixture between 2004 and 2008 in response to soil tillage conditions. LSD = 0.402.
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Table 3 Rhynchosporium area under the disease progress curve (AUDPC) values for each season average and each cultivar–nitrogen average.
N1 N2
2004 59.64 Fanfare 4.08 10.83
2005 46.27 Pastoral 3.90 6.88
2006 15.85 Pipkin 46.81 227.13
2007 9.12 Sumo 6.41 74.42
2008 12.52
2008 score was N2 only. LSD years = 16.62; cultivars × nitrogen = 9.90.
Fig. 9. Comparison of rhynchosporium infection each year on different tillage treatments.
the complex mixtures. However, in 2007 and 2008 the benefits of mixtures were not apparent (−0.7 and 0.4%). The monocultures have significantly different yields and disease resistances and contribute their characteristics in different ways to the mixtures. Beneficial yield responses were generally most evident with cultivars most susceptible to disease - Pastoral and Pipkin; and in the most complex 4-component mixture. However, as the overall mixture effects were small, individual mixture comparisons would not be expected to show significant differences. Thousand grain weight data followed a similar trend to yield, again with few significant differences but a trend towards better weights in the better yielding, more disturbed soil conditions. 3.5. Disease The most common disease was rhynchosporium which was scored in all years. Its severity varied through the season tending to be slightly greater in zero tillage than the other soil treatments early in the season (data not shown). However, differences were inconsistent so Area Under the Disease Progress Curve (AUDPC) scores were analysed as the best reflection of overall damage caused to the crop. In 2004 this comprised four scores, five in 2005, three in 2006, two in 2007 and three in 2008. In 2004 and 2005 rhynchosporium mean scores appeared lowest on deep plough and highest on zero (2004) or minimum (2005) (Fig. 9). A similar pattern was found in 2006 but it was not possible to make reliable comparisons because of big differences in crop densities affecting disease development (data not shown). In 2007 the zero and minimum treatments again had the highest rhynchosporium levels but in 2008 they were the lowest. Mildew occurred at low levels in all years and was only at sufficient severity to be scored in 2006 when it was scored twice. It was greatest in the deep plough treatment, significantly more than the zero and minimum tillage treatments, but this probably reflects nutrient availability differences between treatments due to crop density effects from poor winter survival as such biotrophic pathogens are generally responsive to nitrogen levels. These data are therefore of little use and are not considered further. Raw data were square-root transformed to improve residual distributions. As with yield, nitrogen, cultivar and year were highly significant, as were many interactions. However, soil tillage treatment was clearly not significant, but interaction with year and cultivar was. There was more than five times the rhynchosporium severity in the standard nitrogen treatment compared with the low nitrogen (Table 3). There was also more than four times the rhynchosporium infection in the first two years compared with the subsequent three. Rhynchosporium was disproportionately increased in the more susceptible cultivars, namely Pipkin and Sumo.
Fig. 10. Comparison of the effect of mixtures of different complexity for controlling rhynchosporium under different soil disturbance conditions across all years.
The grouped monoculture and mixture contrasts show most mixtures decreased rhynchosporium in all years and tillage conditions. The means indicate the magnitude of these reductions, ranging from 48 to 77%, the complex mixtures generally being around 32% better than the simple mixtures (Fig. 10). The mean rhynchosporium AUDPC across all the years for the 2-component mixtures, and for the 3- and 4-component mixtures together, was compared with the monoculture mean using a contrast and its standard error (Snedecor and Cochran, 1980) and was found to be always highly significantly different (p < 0.001). There was a trend towards less difference in the minimum and zero tillage treatments (Table 4 and Fig. 11). The reduction in disease was similar in high and low nitrogen treatments overall. As with yield, under standard nitrogen infection in 2004 and 2005 behaved differently from the more mature treatments in 2007 and 2008. In 2007 and 2008 the mixtures always had less infection than the monocultures but some
Fig. 11. Rhynchosporium in mixtures and monocultures showing correlation between disease severity and effect.
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Table 4 Comparison of the effect of mixtures on rhynchosporium levels and yield in barley cultivar mixtures of different complexity under different soil disturbance conditions. Compact
Conventional
AUDPC Monoculture 49.74 2-component 19.16 3- & 4-comp. 11.33 Mean 24.71 LSD (0.05) of means = 8.64 Percentage disease reduction cf. monoculture 61% 2-component 77% 3- & 4-component Yield Monoculture 2-component 3- & 4-component Mean LSD (0.05) of means = 0.26 Percentage yield increase cf. monoculture 2-component 3- & 4-component
Deep
Minimum
Zero
46.60 18.97 12.28 24.11
43.55 15.03 9.69 20.86
48.92 25.29 19.72 29.73
48.98 21.33 15.34 26.71
59% 74%
65% 78%
48% 59%
56% 68%
2.96 2.97 3.01 2.98
3.08 3.11 3.12 3.11
3.05 3.10 3.09 3.08
2.96 2.93 2.99 2.96
2.69 2.76 2.77 2.74
0.3% 1.7%
1.0% 1.3%
1.6% 1.3%
−1.0% 1.0%
2.6% 3.0%
were not significantly different (Fig. 11). However, disease values were much lower in 2007 and 2008 as there were fewer epidemic cycles (Fig. 10). 4. Discussion Cultivar-specific effects of soil cultivation practices were observed on the yield of barley crops over a five year period. Whilst the average yields under high soil disturbance conditions tended to increase from 2004 to 2008, the opposite was observed under zero tillage, resulting in a 20% drop in yield over the same time (Fig. 5). The traditional breeding approach that relies on highly favourable growing conditions may therefore not identify lines that perform better under reduced tillage. All cultivars yielded similarly in response to all soil disturbance treatments but Pastoral was affected most, showing a greater response to minimum tillage treatment but not responding as well as the other cultivars to deep plough conditions. Differences in rankings reflecting these responses increased as the soil conditions developed across the years, Pastoral going from the lowest to the highest yielding cultivar and Fanfare doing the opposite between 2004 and 2008 data. There was little effect on thousand grain weight for any treatment and nitrogen treatment had only effects on the scale of responses (Table 5). Rhynchosporium was a major disease in this trial, mostly in the earlier years. Mildew was recorded at significant levels in the problematic 2006 trial but no disease was recorded at levels likely to affect yield to a great extent in 2006, 2007 or 2008. Rhynchosporium severity was greatest in the standard nitrogen treatments and in the more susceptible cultivars, but again there was no interaction with soil tillage treatment. There was a suggestion in the data that under zero tillage rhynchosporium was more severe early season, or conversely that treatments such as deep plough minimised early season infection, and this would be expected as it would correlate with the amount of crop debris with inoculum (Atkins et al., 2010). In all years except 2008 either or both the minimum and zero tillage treatments had more rhynchosporium overall, but in 2008 the opposite occurred. This may be a reflection
of an equilibrium being established between pathogens and their antagonists as found for eyespot in wheat (Kuntzsch, 1990; Jamaluddin and Jenkyn, 1996; Burnett and Hughes, 2004). Under the different tillage treatments, the distribution of residue, soil physical conditions and weed seed propagation will influence yield responses (George et al., 2009; Arvidsson, 1998). Furthermore, penetrometer resistance >2 MPa is likely to at least halve root elongation rate (Bengough, 1997) and the depth at which this occurred varied between 180 mm and 280 mm in the minimum and deep plough tillage treatments respectively. Before these conditions are discussed, however, it needs to be emphasised that the study was conducted in a temperate, maritime climate. Whereas many studies internationally have demonstrated the benefits of reduced tillage compared to ploughing for carbon (Lal, 2009), biota and physical conditions in soil (Govaerts et al., 2007), the local conditions of this study resulted in dense surface soil and shallow plough or traffic pans developing (personal communication. Bruce Ball, SAC, Edinburgh). Under deep plough, however, this will be off-set by roots accessing water at greater depth (McKenzie et al., 2009). The compaction treatment increased mechanical impedance to rooting and this could explain the small drop in yield compared to ploughing and deep ploughing in some years of the experiment (Bengough, 1997; Atkinson et al., 2007). There were distinct differences in penetration resistance with depth between treatments that reflect the observed changes in yields. With improved traffic guidance systems, opportunities are emerging for controlled traffic to prevent soil compaction occurring in large proportions of cereal fields. Preventing the creation of dense pans in the soil may provide opportunities to reduce tillage under the climatic conditions found here. A major trait used to select the four cultivars grown in this experiment was the root morphology of seedlings. Pipkin seedlings had the longest root length (Fig. 3) and had the smallest yield reduction under zero tillage of all cultivars (Fig. 6), whereas Pastoral seedlings had the shortest root length and had the greatest yield penalty. This cultivar may therefore establish a deeper root system in the field over the winter and spring when soil water contents are large enough for penetration resistance to not limit root elongation. The
Table 5 Mean yields across years and treatments (kg/plot). Year
2004 2.975
2005 3.279
2006 2.450
2007 3.052
2008 3.110
LSD 0.028
Treatment
Compact 2.977
Conventional 3.104
Deep 3.081
Minimum 2.962
Zero 2.742
LSD 0.028
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different cultivars may also have different morphological plasticity of roots in response to soil physical conditions (Bingham and Bengough, 2003). Current research is investigating the response of roots of different cultivars to soil physical conditions in this field experiment. By planting mixtures, increased resilience was evident from smaller shifts in yields between cultivation treatments and growing seasons. Mixtures enhanced yield in 2004 and 2005 in proportion to their complexity as expected from previous data (Newton et al., 1997) but differences were small or not significant in 2007 and 2008. There was no interaction with soil tillage condition in the efficacy of the mixtures on yield or thousand grain weight. As for yield, mixtures had a much more pronounced effect on rhynchosporium infection in 2004 and 2005 compared with the other years, and in 2008 they had no effect, probably a reflection of the very low disease levels in the latter years. As mixtures reduce disease by extending the epidemic cycle length, with few cycles they will have little effect. However, mixtures reduced infection substantially and in similar amounts in proportion to their complexity across all tillage treatments, but showed a tendency towards improved efficacy on minimum and zero tillage treatments. As well as contrasting root and disease resistance traits, cultivars differed in agronomic traits, particularly yield sensitivity. This measures cultivar differential yield responses to soil conditions or site fertility. In the UK Variety Recommended List trial system (hgca.com) this was calculated by determining the relative yields of a panel of cultivars on sites with differing yield potentials, namely 5, 7 and 9 tonnes per hectare, across several consecutive seasons. Yield sensitivity where values greater than 1.0 indicate that a cultivar is more sensitive to changes in site yield/fertility, i.e. it is better able to respond to high yielding conditions. Conversely, a low sensitivity cultivar is likely to perform relatively well on low yield potential sites (NIAB, 2001; Finlay and Wilkinson, 1963). The selected cultivars ranged from 0.80 for Pipkin to 1.06 for Sumo, these being the best yielding cultivars under deep plough and zero tillage treatments respectively (Fig. 6). Thus yield sensitivity may also correlate with degree of soil disturbance presumably making nutrients more available and thereby a proxy for yield potential. The hypothesis that using cultivars complementary in root traits would mimic below ground the complementarity of heterogeneous traits above ground (Newton et al., 2009), was not demonstrated in this work. Some cultivar combinations may have suited particular soil treatments, but if so then the advantages were small and not expressed by their effect on the means. However, the cultivars were selected on seedling root differences and although some interactions between monocultures and soil conditions were found, the differences were not great and therefore the potential complementarity effects may have been small. Selection based on adult plants roots might have been better, but as all roots are highly responsive to soil environments (Passioura, 1991), gross differences may still not have been enough to see significant interactions. A subsequent preliminary screen of many more cultivars has identified ones with strong differential interactions with low and high soil disturbance conditions (Newton, Bengough et al., unpublished data). Unfortunately, the cultivars used in the work reported here were amongst the ones that showed relatively little differential response. Overall we show some differential cultivar response to soil tillage conditions, a buffering of this difference in mixtures, and a benefit of using mixtures expressed in both yield response and disease control under all soil tillage conditions. We have indications that looking at a much wider range of barley genotypes might reveal stronger interactions with soil tillage. If such genotypes can be identified then they may still best be deployed in mixtures as soil conditions are highly variable between seasons, and mixtures enable responsive cultivars to be always in situ to best utilise available resources.
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Acknowledgements We thank the Scottish Government Rural and Environment Science and Analytical Services (RESAS) for funding from the Sustainable Agriculture - Plants programme. We thank Christine Hackett of Biomathematics and Statistics Scotland (BioSS) for statistical advice and analysis. We also thank the farm staff at the Invergowrie site of the James Hutton Institute. References Arvidsson, J., 1998. Effects of cultivation depth in reduced tillage on soil physical properties, crop yield and plant pathogens. Eur. J. Agron. 9, 79–85. Atkinson, B.S., Sparkes, D.L., Mooney, S.J., 2007. Using selected soil physical properties of seedbeds to predict crop establishment. Soil Till. Res. 97, 218–228. Bengough, A.G., 1997. Modelling rooting depth and soil strength in a drying soil profile. J. Theor. Biol. 186, 327–338. Bengough, A.G., Gordon, D.C., Al-Menaie, H., Ellis, R.P., Allan, D., Keith, R., Thomas, W.T.B., Forster, B.P., 2004. 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